Within the packaging technology, use is often made of consumer packages of single-use disposable type for packing and transporting liquid foods. The demands placed on such so-called single-use disposable packages is that they must be easy to produce and handle and that they, moreover, impart to their packed product the requisite product protection in order to be able to store the product in an unopened package without the risk that the product deteriorate and become unfit for consumption.
The requirement on requisite product protection is, of course, particularly important when the product which is to be packed is a food, and in order to make for reliable handling of a packed food, use is therefore most generally made of so-called aseptic packages which are a special type of the above-mentioned single-use packages. An aseptic package differs from a corresponding non-aseptic package principally in that the aseptic package, prior to filling, is subjected to a bactericidal treatment (e.g. a sterilisation treatment) and that the thus treated package is thereafter filled and sealed under sterile conditions in order to reduce the risk of re-infection.
Aseptic single-use packages are produced, for example, from a web of a packaging material in that the web is, for the purpose of sterilisation, led through a bath of aqueous hydrogen peroxide solution and thereafter reformed into packages which are filled with the pertinent, separately sterilised product and sealed in a sterile filling atmosphere. The entire production cycle, including the sterilisation, is put into effect with the aid of modern, rational packaging and filling machines of the type which both form, fill and seal aseptic packages at a product output speed of several thousands of packages per hour, practically round the clock, without disruption other than for planned normal operational maintenance.
Since such high production output speeds require correspondingly extremely high web speeds, it is obvious that the contact of the web with the sterilising hydrogen peroxide bath will be only brief, unless the bath is extended to an excessive length. In order to achieve the desired sterilisation effect at these high production output speeds, it is therefore important that all parameters relevant for the sterilisation, e.g. temperature, concentration etc., are monitored and maintained at their predetermined levels throughout the entire production cycle in order to avoid unnecessary production waste because of insufficient sterilisation of the web.
In the described, prior art packaging production, the temperature and hydrogen peroxide concentration of the sterilisation bath are set initially at their respective levels for the desired sterilisation of the web at the current web speed, whereafter the temperature of the bath is continuously monitored during the sterilisation, while the concentration of the bath is only monitored at predetermined time intervals, e.g. after four or eight hours. Such an intermittent monitoring is unsatisfactory and can, in the worst case scenario, lead to all packages produced during the meantime having to be rejected (product waste) if it proves at the time of monitoring that the concentration drastically or prohibitively deviates from the predetermined concentration level.
Another drawback inherent in the prior art sterilisation method is that it requires careful and complete removal of hydrogen peroxide from the web after passage through the hydrogen peroxide bath in order to eliminate the risk that hydrogen peroxide accompanies the web and finally comes into contact with the product which is to be packed.
Efficient removal of hydrogen peroxide from the web is, as a rule, easy to achieve in such cases where the web is entirely smooth, but is more difficult if the web displays irregularities on its surface, e.g. applied opening strips etc., where the hydrogen peroxide may readily penetrate in and become inaccessible. The problem with residual quantities of hydrogen peroxide in the sterilise web is further aggravated in those cases where the web displays incision edges with exposed paper or paperboard fibre which readily absorb and conceal residual quantities of hydrogen peroxide in the fibre layer of the web.
The problem in connection with hydrogen peroxide in a packaging material which, for the purpose of sterilisation, has been in contact with an aqueous hydrogen peroxide solution is wholly obviated by another prior art sterilisation method in which the packaging material, for the purpose of sterilisation, is irradiated with emitted electrons from an electron radiation source which directs electron beams at at least those parts of the packaging material which later come into contact with a product packed in the sterilised packaging material.
A sterilisation method which employs electron irradiation instead of hydrogen peroxide as the sterilisation agent is extremely rapid and efficient in the sterilisation of packaging material and/or ready-to-fill packages, but none of the hitherto prior art electron irradiation methods has a system for the continuous monitoring and control of the sterilisation throughout the entire sterilisation process. In particular, the prior art electron irradiation methods lack a system which is capable of responding instantaneously to a detected deviation in a monitored process parameter and immediately thereafter activating a control unit for correcting the deviating parameter back to the correct level, at the same time as only that part of the packaging material which had been sterilised at the incorrect parameter level is automatically rejected without needing to stop the sterilisation process.